“Soft errors” in electronic circuitry are signals that represent erroneous data, but not due to an error in the design or operation of the circuitry. For example, electrical or magnetic interference inside a computer system can cause a single bit of dynamic random-access memory (DRAM) to spontaneously flip to the opposite state.
DRAM is ubiquitous in personal computers, workstations, and servers, and is normally included on one or more memory modules. Memory modules take many forms, but each includes a number of individual DRAM components mounted on a printed-circuit board (PCB). Some DRAM modules include extra storage for “syndromes,” information calculated for each unit of stored data and used in support of error-correcting codes (ECC). Depending on the code, the syndromes may support single- or multi-bit correction, or even accommodate the loss of an entire memory component.
DRAM modules may provide the stored syndromes with the corresponding data to a memory controller that performs the error correction. Memory controllers with error-correction capability are relatively expensive, however. Though less common, memory modules may themselves include circuitry that performs error correction, and thus allows them to be used with less expensive memory controllers. Module-based error-correction is expensive, however, and can introduce considerable and undesirable read and write delays. There is therefore a need for fast and economical correction for soft errors.
The figures are illustrations by way of example, and not by way of limitation. Like reference numerals in the figures refer to similar elements.